Heretofore, a flash memory has been known as one of non-volatile memory devices. The memory cell of the flash memory has a structure comprising a floating gate formed on a substrate via a tunnel oxide film, and a control gate formed via a gate insulation film, which are laminated with each other. In an operation of the memory cell, upon writing, electrons (or positive holes) are injected from a drain of the memory cell to the floating gate by using a voltage difference between the control gate and the drain.
On the other hand, upon erasing, electrons (or positive holes) in the floating gate are released into the drain by using a controlled voltage difference between the control gate and the drain. Assuming a substrate as P type, and a source and a drain as n type, a channel of the memory cell becomes off state in case that the floating gate has electrons, and on state in case that it has no electron, so that it operates as a non-volatile memory.
As conventional flash memories, FLOTOX (floating-gate tunnel oxide) types and MNOS (metal nitride oxide semiconductor) type are known. FLOTOX type has a structure comprising a tunnel oxide film (first gate insulation film), a floating gate, an interlayer insulation film (second gate insulation film), and a control gate laminated on a channel formed on a surface of a semiconductor substrate, and accumulates electric charges in the floating gate or releases them into the channel by applying controlled voltage difference either to generate an accumulated state or an erased state, and carry out writing and reading of 1 bit information by using the accumulated state and the erased state. MNOS type has a structure comprising two layers of insulation film made of oxide film (silicon oxide film) and nitride film, and accumulates electric charges into the trap of interface of two films thereof.
Also in contrast to those electrical memory, there are a mechanical non-volatile memory, for example, using a mechanical pendulum and others, which is seemed to be technologically closest in the field of realizing mechanical memory to the present invention (for example, see Physical Review Letters, Vol. 87, p. 096101-1, 2001.).
General description of Electrical flash memories are described in various journals (for example, see Electronic Materials, Kogyo Chosakai, April, 1993, p. 32, or LSI Handbook, Ohmsha, edited by The Institute of Electronics, Information, and Communication Engineers, Nov. 30, 1984, p. 485.). However, in the above-mentioned electrical flash memories, the material existing between the floating gate and the drain, through which the electric current of writing flows, is deteriorated by the current, and the repetition of the writing causes the formation of leakage current path between the floating gate and the drain, thereby a restriction for the times capable of writing arises. That is, since the electrons or positive holes accumulated in the floating gate flow out through the leakage current path formed by the repetition, there is a problem to be solved that the repetition of writing causes the memory not to operate as a non-volatile memory.
The object of the present invention is to provide an information memory device capable of writing an information by mechanical operation of a floating gate layer, a method of manufacturing the same, and a memory array of using it, by which the above problem can be solved.